Variable stator vane assembly for an axial flow compressor of a gas turbine engine

ABSTRACT

A variable angle stator vane assembly for an axial flow gas turbine engine compressor. The compressor casing has a bore surrounded by a boss at the position of each assembly. A housing having a central bore and a bushing assembly is located in the casing bore and is bolted to the boss. The stator vane spindle extends through the housing bore and busing assembly. The housing and bushing assembly can be removed from the casing bore, to be rotated 180° or replaced, without removing the casing from the compressor or the stator vane spindle from the casing bore.

This application is a continuation of application Ser. No. 07/801,135,filed Dec. 2, 1991.

TECHNICAL FIELD

The invention relates to a variable stator vane assembly for a gasturbine engine axial flow compressor, and more particularly to such anassembly wherein the bearing assembly for the stator vane can be rotatedaxially 180° for prolonged service life and can be removed and replacedfrom the exterior of the compressor casing without removal of the casingor the stator vane.

BACKGROUND OF THE INVENTION

In the typical gas turbine engine, the axial flow compressor comprises arotor surrounded by a casing. The casing is generally made in twohalves, removably joined together. The rotor is made up of a pluralityof stages, each comprising a rotor disc with a single row of bladeslocated on its outer rim. The stages are joined together and to aturbine driven shaft. The casing supports a plurality of stages orannular rows of stator vanes. The stator vane stages are located betweenthe compressor blade stages, helping to compress the air forced throughthe compressor and directing the air flow into the next stage of rotorblades at the proper angle to provide a smooth, even flow through thecompressor.

It has long been known that the use of variable stators to control theamount of air flowing through the compressor will optimize theperformance of the compressor throughout the entire operating range ofthe engine. To this end, selected stator vane stages (generally at theforward portion of the compressor) are provided with variable statorvanes. In the usual prior art practice, at the position of each variablestator vane the casing is provided with an opening or bore surrounded byan exterior boss. The variable stator vane, itself, has a base portionand/or a shaft portion which extends through the bore and is rotatabletherein. A bearing assembly is provided in association with the bore toprevent wear of the casing and the stator vane.

Through appropriate testing, a stator schedule is developed whichoptimizes performance of the compressor, while maintaining acceptablestall margins, throughout the range of operation of the engine. Anactuation system is provided to rotate and reposition the stator vanesof each variable stator vane stage according to the stator schedule.

In the usual practice, a circumferentially shiftable unison ring isprovided for each variable stage and surrounds the casing. Each variablestator vane of each variable stage has a lever arm operatively connectedto its respective unison ring. The unison rings are shifted by anappropriate drive or bell crank mechanism operated by an appropriateactuator, as is well known in the art.

The above-mentioned bushing assemblies, designed to protect eachvariable stator vane and the adjacent portion of the casing, are, ofcourse, subject to wear. This can lead to metal-to-metal contact betweena variable stator vane and the compressor casing. Excessivemetal-to-metal contact increases friction in the variable vane system,which in turn can prevent or interfere with movement of the vanes whichcould result in engine stall. The bushing assembly wears as the variablestator vane is pivoted during engine operation. Some portions of thebushing assembly which are highly loaded tend to wear more than otherless highly loaded portions. In prior art structures, unacceptable wearhas been detected within from about 6,000 to 10,000 hours of engineoperation.

Maintenance to replace the bushing assembly involves removing thecompressor casing and tearing down the variable stator vane assembly.This is expensive, time consuming, and requires skilled workers.

The present invention provides a bushing assembly in a metal housing.The bushing assembly is preferably an integral, one-piece bushing,although a multi-piece bushing can be used, as will be describedhereinafter. The housing/bushing assembly is bolted to the compressorcasing, and can be removed and replaced without opening and removing thecasing, and without removing the variable stator vane. As a result, thebushing assembly can be removed and replaced less expensively, morerapidly and requires less skill to perform.

Furthermore, the housing/bushing assembly can be axially rotated 180°.As a consequence, wear on the bushing assembly ca be distributed aroundthe circumference thereof, greatly increasing its service life. It isanticipated that bushing assembly life can be extended to about 25,000hours.

SUMMARY OF THE INVENTION

According to the invention there is provided a variable angle statorvane assembly for use in an axial flow gas turbine engine compressorhaving a rotor surrounded by a casing. The rotor provides a plurality ofstages of rotating compressor blades and the casing mounts a pluralityof stages of stator vanes located between the stages of rotor blades.Selected stages of stator vanes are provided with variable angle statorvane assemblies to adjustably direct air flow to the adjacent compressorblade stage. At the position of each variable angle stator vaneassembly, the compressor casing is provided with a bore surrounded onthe exterior of the casing by an outwardly extending boss. A cylindricalhousing is located within the casing bore. The housing has an inner endand an outer end. The housing outer end is provided with a lateralflange overlying and bolted to the casing boss. The housing has a borecoaxial with the casing bore. The housing bore has a first long portionextending from the housing inner end toward the housing outer end and asecond shorter portion extending through said outer end and of largerdiameter, forming a shoulder between the first and second bore portions.The housing supports a busing assembly having a central cylindricaljournal bearing portion within said first bore portion. Said bushingassembly having a first thrust bearing portion overlying the inner endof said housing. Said bushing assembly having a second thrust bearingportion overlying the housing shoulder.

The variable stator vane has a base portion abutting the first thrustbearing portion of the bushing assembly. The variable stator vane has aspindle portion rotatively received and extending through the journalbearing portion of the bushing assembly.

The spindle extends through a central perforation in a circular spacerhaving a diameter such that the spacer is received in the largerdiameter outer portion of the housing bore. The spindle also passesthrough a cylindrical alignment sleeve. The outermost end of the shaftis threaded and the assembly is held together by a hex nut threadedlyengaged on the vane shaft. The hex nut abuts the alignment sleeve andcauses the spacer to bear against the outer thrust bearing portion ofthe bushing assembly. The variable stator vane shaft also passes throughan opening in one end of a lever arm which overlies the hex nut andwhich is held in place by an additional nut threadedly engaged on theshaft. Means are provided to render the lever arm non-rotatable withrespect to the spindle.

From the above description it will be apparent that upon removal of thesecond nut, the lever arm, the hex nut, the alignment sleeve and thespacer, the bearing assembly housing can be unbolted from the casingboss and either rotated 180° or removed and replaced, depending upon thecondition of the bearing assembly. Turning or replacement of the bearingassembly housing can be accomplished from the exterior of the compressorcasing without removal of the compressor casing or the variable statorvane.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing anddistinctly claiming the present invention, it is believed the same willbe better understood from the following description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a fragmentary cross-sectional elevational view of an exemplaryprior art variable stator vane assembly;

FIG. 2 is a fragmentary, cross-sectional, elevational view of thevariable stator vane assembly of the present invention;

FIG. 3 is a plan view of the bushing assembly and its housing;

FIG. 4 is a cross-sectional view taken along section line 4--4 of FIG.3;

FIG. 5 is a cross-sectional view, similar to FIG. 4, and illustrating analternate form of bushing assembly; and

FIG. 6 is a fragmentary, cross-sectional, exploded elevational view ofthe variable stator vane assembly of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like numerals indicate the sameelements throughout the views, FIG. 1 illustrates an exemplary prior artvariable stator vane assembly. In FIG. 1 the stator vane is indicated at1 and is shown located between a pair of compressor blades 2 and 3representing adjacent compressor stages. The compressor casing isillustrated at 4 and is provided with an outwardly extending boss 5. Thecompressor casing is provided with a bore 6 having an inner portion 6a,an intermediate portion 6b of lesser diameter, and an outer portion 6chaving a diameter greater than the portion 6b and slightly less than theportion 6a. An annular shoulder 7 is formed between bore portions 6a and6b. A second annular shoulder 8 is formed between bore portions 6b and6c.

The variable stator vane 1 has a base 9 provided with an annular portion10 and a central spindle 11. The spindle 11 has a first portion 11aterminating in a second threaded portion 11b of lesser diameter.

The base portion 9, annular portion 10 and spindle 11 extend into andthrough the casing bore 6. A composite thrust washer 12 is locatedbetween the base 9 and the annular shoulder 7. A composite bushing 13 isalso provided. The composite bushing 13 has a cylindrical journalbearing portion 13a located between the bore portion 6b and the annularportion 10 of the variable stator blade base 9. The bushing 13 also hasan annular thrust washer portion 13b overlying the shoulder 8.

The stator vane spindle portion 11a extends through a perforation 14 ina spacer 15. The spacer 15 has a circular peripheral configuration and adepending outer rim portion 15a which faces the portion 13b of bushing13.

The portion 11a of spindle 11 also passes through a perforation 16through one end of a lever arm 17. Spindle portion 11a has a flat formedthereon (not shown) and the perforation 16 is correspondinglyconfigured, so that the lever arm 17 is non-rotatable with respect tothe spindle portion 11a. The lever arm 17 is operatively connected tothe variable stator vane actuation system (not shown) describedheretofore. The spindle 11 passes through an alignment sleeve 18 and theassembly thus far described is held together by a nut 19 threadedlyengaged on the spindle portion 11b. When nut 19 is tightened, the outerend of annular portion 10 abuts spacer 15 assuring a running clearancebetween the base 9 and the thrust washer 12 as well as between thedepending outer rim portion 15a of the spacer 15 and the portion 13b ofbushing 13.

From the above description, it will be apparent that in order to replacethe thrust washer 12 and bushing 13, it is necessary to remove thecasing 4 from the compressor section of the engine and to remove thevariable stator vane base elements 9, 10 and 11 from the casing bore 6.

Reference is now made to FIG. 2 wherein the variable stator vaneassembly of the present invention is illustrated. The variable statorvane is indicated at 20 and is located between a pair of compressorblades 21 and 22, representing adjacent compressor stages.

The compressor casing is illustrated at 23 and is provided with a high,upstanding boss 24. The boss 24 has a rectangular peripheralconfiguration. A bore 25 is located centrally of the boss. The bore 25has a first portion 25a and a second portion 25b of lesser diameter,forming a shoulder 26 therebetween.

The embodiment of FIG. 2 also includes a housing 27. The housing 27 isalso shown in FIGS. 3 and 4 The housing 27 is a metal member having acylindrical body 27a. At its inner end, the body 27a terminates in aplanar, annular bottom surface 27b. At its outer end, the body 27a isprovided with a lateral flange 27c having a rectangular peripheralconfiguration.

The housing 27 has a central bore 28. The bore 28 has a first portion28a and a second portion 28b of greater diameter. An annular shoulder 29is formed between the two bore portions.

The housing 27 supports a bushing assembly 30. The bushing assembly 30preferably constitutes an integral, one-piece structure and is made ofany material appropriate for this use. Excellent results have beenobtained using a woven fabric impregnated with resin and formed directlywithin the housing 27. Under these circumstances, the resin bonds thebushing assembly 30 to the housing 27. The bushing assembly has ajournal bearing cylindrical portion 30a. The bushing assembly portion30a terminates at its inner end in an annular thrust bearing portion 30boverlying the inner end 27b of housing 27. The bushing assembly portion30a terminates at its outer end in an annular thrust bearing portion 30cwhich overlies the housing shoulder 29.

The housing body 27a has an external diameter equivalent to the internaldiameter of the casing bore portion 25b and is receivable therein, as isshown in FIG. 2. The flange 27c of housing 27 is adapted to overlie thehigh boss 24 of the compressor casing 23. The housing flange 27c has apair of perforations 31 and 32 located in opposite corners thereof. Thecompressor casing boss 24 is provided with a pair of threaded bores (notshown) coaxial with the flange perforations 31 and 32, respectively. Apair of bolts 33 and 34 extend through the perforations 31 and 32 andthreadedly engage in the threaded boss bores (not shown) to secure thehousing 27 in its mounted position as shown in FIG. 2. The bolt 34 isshown in phantom lines in FIG. 2 since it would not normally be visiblein this figure.

The adjustable stator vane 20 is provided with a base 35 and anupstanding spindle 36. The spindle 36 has a first portion 36a, a secondportion 36b of lesser diameter, and a third portion 36c of yet lesserdiameter. The third portion 36c is externally threaded, as shown in FIG.2. A shoulder 36d is formed between spindle portions 36a and 36b. Thebase 35 of the variable stator vane 20 is receivable with clearance inthe bore portion 25a of the casing bore 25. It will be noted that thethrust bearing portion 30b of bushing assembly 30 is located between thevariable stator vane base 35 and the inner annular end surface 27b ofhousing 27. The first spindle portion 36a is of a diameter approximatingthe internal diameter of the journal bearing portion 30a of bushingassembly 30 and is rotatively received therein.

A disc-like spacer 37 has a peripheral diameter slightly less than thediameter of housing bore portion 28b and is receivable therein,overlying the thrust bearing portion 30c of bearing assembly 30. It willbe noted that the periphery of spacer 37 is relieved as at 37a toprovide clearance for the heads of bolts 33 and 34. The spacer 37 has acentral perforation 38 through which the spindle portion 36b extendswith clearance. The spacer 37 is surmounted by an alignment sleeve 39having a central bore 40, coaxial with the spacer perforation 38. Thevariable stator vane spindle portion 36b extends into the bore 40 ofalignment sleeve 39. Spindle portion 36b has a number of flats (notshown) formed thereon and the alignment sleeve bore 40 iscorrespondingly configured to render the alignment sleeve non-rotatablewith respect to the spindle 36.

The elements thus far described are held in place by a hex nut 41,threadedly engaged on the threaded shaft portion 36c and abutting thealignment sleeve 39. When the hex nut 41 is tightened, the spacer 37abuts the spindle shoulder 36d assuring a running clearance between thebase 35 and bushing portion 30b as well as between the spacer 37 andbearing portion 30c.

The threaded portion 36c of shaft 36 extends through a perforation 42 ina lever arm 43. The alignment sleeve 39 is provided with threeperipheral flats, one of which is shown at 39a in FIG. 2. Each of thealignment sleeve flats is engaged by a depending tab on the lever arm43. One such tab is shown at 43a in FIGS. 2 and 6. A second one of thetabs is shown at 43b in FIG. 6. This arrangement assures that the leverarm 43 is non-rotatable with respect to the alignment sleeve 39. Sincethe alignment sleeve 39 is non-rotatable with respect to spindle 36, thelever arm 43 is also non-rotatable with respect thereto. The other endof lever arm 43 (not shown) is operatively attached to the variablestator vane actuation system, described above. The lever arm 43 is heldin place by a nut 44 threadedly engaged on shaft portion 36c.

It would be within the scope of the present invention to provide amulti-piece bearing assembly of any appropriate bearing material such asa carbon composite material, rather than the one-piece bearing assembly30. This is illustrated in FIG. 5. The housing of FIG. 5 is designatedby index numeral 45 and is essentially identical to the housing 27 ofFIG. 4. To this end, the housing 45 is a metallic member having acylindrical body 45a, terminating at its inner end in a planar, annularbottom surface 45b. At its outer end, the body 45a is provided with alateral flange 45c identical to the flange 27c of FIG. 4. As in the caseof the housing 27 of FIG. 4, the housing 45 of FIG. 5 has a central bore46 having a first portion 46a and a second portion 46b of greaterdiameter, an annular shoulder 47 being formed therebetween.

In this instance, the bushing assembly comprises a cylindrical journalbearing 48, an inner thrust washer 49 and an outer thrust washer 50. Thecylindrical journal bearing 48 and the outer thrust washer 50 are heldin place by an interference fit. The inner thrust washer 49 ismaintained in place by an annular swaged area 51 about the inner surface45b of housing 45. Alternatively, the annular swaged area 51 could bereplaced by an annular bead of solder or the like. It will be understoodby one skilled in the art that the housing 45 and its bushing elements48, 49 and 50 could be readily substituted in the assembly of FIG. 2 forthe housing 27 and the bearing assembly 30.

The invention having been described in detail, the manner in which thehousing 27 and its bearing assembly 30 can be rotated 180° or replaced,can now be set forth. Reference is made to FIG. 6 which is an explodedview of the structure of FIG. 2 and wherein like parts have been givenlike index numerals.

To rotate or remove and replace the housing 27 and bearing assembly 30,the nut 44 is first removed, enabling disengagement of the lever arm 43from spindle 36 and alignment sleeve 39. Hex nut 41 is thereafterremoved from the threaded portion 36c of spindle 36, permitting removalof alignment sleeve 39. At this point, the bolts 33 and 34, affixinghousing 27 to boss 24, are removed. The spacer 37 can now be removed, orcan simply be removed with the housing 27.

To assist in removal of the housing 27 from the boss bore 25, it iswithin the scope of the invention to provide the housing flange 27c witha pair of threaded bores 52 and 53 (see FIG. 3). The threaded bores 52and 53 enable the use of jack screws (not shown) to assist in liftingthe housing 27 from the bushing bore 25.

Once the housing 27 has been removed, it can be rotated 180° andrepositioned in the boss bore 25, or it and its bushing assembly 30 canbe replaced, depending upon the condition of the bushing assembly.Thereafter, the spacer 37 is reinstated and the housing 27 is affixed tothe boss 24 by the bolts 33 and 34. The alignment spacer 39 is mountedon spindle 30, followed by hex nut 41. The lever arm 43 is mounted onspindle 36 with its tangs engaged on the flats of alignment sleeve 39and the nut 44 is again threadedly engaged on the portion 36c of spindle36.

From the above, it will be apparent that rotation or replacement of thehousing 27 and its bushing assembly 30 can be accomplished quickly andeasily. Furthermore, rotation or replacement of the housing 27 andbushing assembly 30 can be accomplished from the exterior of thecompressor casing 23, without the necessity of removing the compressorcasing 23 from the compressor and removing the variable stator vanespindle 36 from the bushing bore 25.

Modifications may be made in the invention without departing from thespirit of it.

What is claimed is:
 1. A variable angle stator vane assembly for use inan axial flow compressor of a gas turbine engine having a compressorcasing with a bore formed therein at the position of said variable anglestator vane assembly, said variable angle stator vane assemblycomprising: an upstanding external boss integrally formed on said casingand surrounding said casing bore, a housing having a central bore, abushing assembly in said housing, said housing having a body mounted insaid casing bore and an integrally formed lateral flange overlying andremovably affixed to said external casing boss, said variable anglestator vane having a base terminating in a spindle rotatively mounted insaid bushing assembly, said housing and bushing assembly thereof beingremovable and replaceable from the exterior of said casing withoutremoving said casing from said compressor or said stator vane spindlefrom said casing bore.
 2. The variable angle stator vane assemblyclaimed in claim 1, wherein said housing is so configured that saidhousing and said bushing assembly thereof can be removed from saidcasing bore, rotated axially 180°, and reinstalled in said casing borefrom the exterior of said casing without removing said casing from saidcompressor or said stator vane spindle from said casing bore.
 3. Thevariable angle stator vane assembly claimed in claim 1, wherein saidhousing body is cylindrical, terminating in an inner, planar, annularend and an outer end surrounded by said housing flange, said housingbore having a first portion extending from said inner end and a secondportion leading to said outer end, said second bore portion being ofgreater diameter than said first bore portion with an annular shoulderformed therebetween, said annular shoulder facing said outer end, saidbushing assembly comprising a cylindrical journal bearing portionlocated in said first bore portion, an inner thrust bearing portionoverlying said inner end, and an outer thrust bearing portion overlyingsaid housing shoulder.
 4. The variable angle stator vane assemblyclaimed in claim 3, wherein said bushing assembly comprises an integral,one-piece structure formed within and adhered to said housing.
 5. Thevariable angle stator vane assembly claimed in claim 3, wherein saidbushing assembly journal bearing portion and inner and outer thrustbearing portions comprise separate components.
 6. The variable anglestator vane assembly claimed in claim 3, wherein said stator vane basefaces said bushing assembly inner thrust bearing portion overlying saidhousing inner end, said stator vane spindle having a first portionextending through said housing bore first portion and said bushingassembly journal bearing portion therein, said spindle first portionterminating in a second portion of lesser diameter than said firstportion forming an annular shoulder therebetween, said spindle secondportion terminating in a third portion of lesser diameter than saidsecond portion, said third portion being externally threaded, a spacerhaving a central perforation, said spindle second portion extendingthrough said spacer perforation, said spacer overlying said bushingassembly outer thrust bearing portion and abutting said spindle annularshoulder, an alignment sleeve having a central perforation, saidalignment sleeve surrounding said spindle second portion and abuttingsaid spacer, a nut threadedly engaged on said spindle third portion andabutting said alignment sleeve, a stator vane actuating lever arm havinga perforation formed therein and being mounted on said spindle thirdportion abutting said first nut, means rendering said lever armnon-rotatable with respect to said spindle, a second nut threadedlyengaged on said spindle third portion and abutting said lever arm, saidspindle first portion being of such length as to assure runningclearance between said spindle base and said bushing assembly innerthrust bearing portion and between said spacer and said bushing assemblyouter thrust bearing portion.
 7. The variable angle stator vane assemblyclaimed in claim 4, wherein said bushing assembly comprises a wovenfabric impregnated with resin.
 8. The variable angle stator vaneassembly claimed in claim 5, wherein said bushing assembly componentscomprise composite carbon components.
 9. The variable angle stator vaneassembly claimed in claim 6, wherein said housing is so configured thatsaid housing and said bushing assembly thereof can be removed from saidcasing bore, rotated axially 180°, and reinstalled in said casing borefrom the exterior of said casing without removing said casing from saidcompressor or said stator vane spindle from said casing bore.
 10. Thevariable angle stator vane assembly claimed in claim 9, wherein saidbushing assembly comprises an integral, one-piece structure formedwithin and adhered to said housing.
 11. The variable angle stator vaneassembly claimed in claim 9, wherein said bushing assembly journalbearing portion and inner and outer thrust bearing portions compriseseparate components.
 12. The variable angle stator vane assembly claimedin claim 10, wherein said bushing assembly comprises a woven fabricimpregnated with resin.
 13. The variable angle stator vane assemblyclaimed in claim 11, wherein said bushing assembly components comprisecomposite carbon components.